Stent coating apparatus using focused acoustic energy

ABSTRACT

An apparatus for coating a stent includes an optical feedback system used to align a transducer with a stent strut. Once alignment is achieved, the transducer causes a coating to be ejected onto the stent strut and the transducer is moved along the stent strut to coat the stent strut.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a divisional of application Ser. No. 11/305,662,filed Dec. 16, 2005, which is incorporated herein by reference.

TECHNICAL FIELD

This invention relates generally to stent coating apparatuses, and moreparticularly, but not exclusively, provides an assembly and method forcoating of an abluminal stent surface by dispensing coating usingacoustic energy.

BACKGROUND

Blood vessel occlusions are commonly treated by mechanically enhancingblood flow in the affected vessels, such as by employing a stent. Stentsact as scaffoldings, functioning to physically hold open and, ifdesired, to expand the wall of affected vessels. Typically stents arecapable of being compressed, so that they can be inserted through smalllumens via catheters, and then expanded to a larger diameter once theyare at the desired location. Examples in the patent literaturedisclosing stents include U.S. Pat. No. 4,733,665 issued to Palmaz, U.S.Pat. No. 4,800,882 issued to Gianturco, and U.S. Pat. No. 4,886,062issued to Wiktor.

FIG. 1 illustrates a conventional stent 10 formed from a plurality ofstruts 12. The plurality of struts 12 are radially expandable andinterconnected by connecting elements 14 that are disposed betweenadjacent struts 12, leaving lateral openings or gaps 16 between adjacentstruts 12. The struts 12 and the connecting elements 14 define a tubularstent body having an outer, tissue-contacting surface and an innersurface.

Stents are being modified to provide drug delivery capabilities. Apolymeric carrier, impregnated with a drug or therapeutic substance iscoated on a stent. The conventional method of coating is by, forexample, applying a composition including a solvent, a polymer dissolvedin the solvent, and a therapeutic substance dispersed in the blend tothe stent by immersing the stent in the composition or by spraying thecomposition onto the stent. The solvent is allowed to evaporate, leavingon the stent strut surfaces a coating of the polymer and the therapeuticsubstance impregnated in the polymer. The dipping or spraying of thecomposition onto the stent can result in a complete coverage of allstent surfaces, i.e., both luminal (inner) and abluminal (outer)surfaces, with a coating. However, having a coating on the luminalsurface of the stent can have a detrimental impact on the stent'sdeliverability as well as the coating's mechanical integrity. Moreover,from a therapeutic standpoint, the therapeutic agents on an innersurface of the stent get washed away by the blood flow and typically canprovide for an insignificant therapeutic effect. In contrast, the agentson the outer surfaces of the stent are in contact with the lumen, andprovide for the delivery of the agent directly to the tissues. Polymersof a stent coating also elicit a response from the body. Reducing theamount to foreign material can only be beneficial.

Briefly, an inflatable balloon of a catheter assembly is inserted into ahollow bore of a coated stent. The stent is securely mounted on theballoon by a crimping process. The balloon is inflated to implant thestent, deflated, and then withdrawn out from the bore of the stent. Apolymeric coating on the inner surface of the stent can increase thecoefficient of friction between the stent and the balloon of a catheterassembly on which the stent is crimped for delivery. Additionally, somepolymers have a “sticky” or “tacky” consistency. If the polymericmaterial either increases the coefficient of friction or adherers to thecatheter balloon, the effective release of the stent from the balloonafter deflation can be compromised. If the stent coating adheres to theballoon, the coating, or parts thereof, can be pulled off the stentduring the process of deflation and withdrawal of the balloon followingthe placement of the stent. Adhesive, polymeric stent coatings can alsoexperience extensive balloon sheer damage post-deployment, which couldresult in a thrombogenic stent surface and possible embolic debris. Thestent coating can stretch when the balloon is expanded and maydelaminate as a result of such shear stress.

Another shortcoming of the spray coating and immersion methods is thatthese methods tend to form defects on stents, such as webbing betweenadjacent stent struts 12 and connecting elements 14 and the pooling orclumping of coating on the struts 12 and/or connecting elements 14. Inaddition, spray coating can cause coating defects at the interfacebetween a stent mandrel and the stent 10 as spray coating will coat boththe stent 10 and the stent mandrel at this interface, possibly forming aclump. During removal of the stent 10 from the stent mandrel, this clumpmay detach from the stent 10, thereby leaving an uncoated surface on thestent 10. Alternatively, the clump may remain on the stent 10, therebyyielding a stent 10 with excessive coating.

Another shortcoming of the spray coating method is that a nozzle in aspray coating apparatus can get clogged with particulate when some ofthe coating substance solidifies. This clogging can deflect or block thespray, thereby yielding an unsatisfactory coating on the stent 10. Theneed to unclog a nozzle can cause long periods of downtime for a spraycoating apparatus, thereby lowering production rates of stents.

Accordingly, a new apparatus and method are needed to enable selectivecoating of stent surfaces while minimizing the formation of defects andcoating apparatus downtime.

SUMMARY OF THE INVENTION

Briefly and in general terms, the present invention is directed to astent coating apparatus. In aspects of the present invention, anapparatus comprises a transducer capable of ejecting droplets of acoating substance from a reservoir, and an optical feedback system thataligns the transducer with a stent strut such that the coating substanceis delivered to a stent strut.

BRIEF DESCRIPTION OF THE DRAWINGS

Non-limiting and non-exhaustive embodiments of the present invention aredescribed with reference to the following figures, wherein likereference numerals refer to like parts throughout the various viewsunless otherwise specified.

FIG. 1 is a diagram illustrating a conventional stent;

FIG. 2 is a block diagram illustrating a stent coating apparatusaccording to an embodiment of the invention;

FIG. 3 is a block diagram illustrating a stent coating apparatusaccording to another embodiment of the invention;

FIG. 4A and FIG. 4B (collectively, FIG. 4) are diagrams illustratingcross sections of an ejector according to an embodiment of theinvention;

FIG. 5 is a block diagram illustrating a stent coating apparatusaccording to another embodiment of the invention;

FIG. 6 is a is a diagram illustrating a cross section of an ejectoraccording to another embodiment of the invention;

FIG. 7 is a is a diagram illustrating a cross section of an ejectoraccording to another embodiment of the invention; and

FIG. 8 is a flowchart illustrating a method of coating an abluminalstent surface.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

The following description is provided to enable any person havingordinary skill in the art to make and use the invention, and is providedin the context of a particular application and its requirements. Variousmodifications to the embodiments will be readily apparent to thoseskilled in the art, and the generic principles defined herein may beapplied to other embodiments and applications without departing from thespirit and scope of the invention. Thus, the present invention is notintended to be limited to the embodiments shown, but is to be accordedthe widest scope consistent with the principles, features and teachingsdisclosed herein.

FIG. 2 is a block diagram illustrating a stent coating apparatus 200according to an embodiment of the invention. The apparatus 200,including a stent mandrel fixture 20 for supporting the stent 10, isillustrated to include a support member 22, a mandrel 24, and anoptional lock member 26 (e.g., if the stent 10 can be supported by themandrel 24 itself). The support member 22 can connect to a motor 30A soas to provide rotational motion about the longitudinal axis of the stent10, as depicted by arrow 32, during a coating process. Another motor 30Bcan also be provided for moving the support member 22 in a lineardirection, back and forth, along a rail 34.

The support member 22 includes a coning end portion 36, taperinginwardly. In accordance with one embodiment of the invention, themandrel 24 can be permanently affixed to coning end portion 36.Alternatively, the support member 22 can include a bore 38 for receivinga first end of the mandrel 24. The first end of mandrel 24 can bethreaded to screw into the bore 38 or, alternatively, can be retainedwithin the bore 38 by a friction fit. The bore 38 should be deep enoughso as to allow the mandrel 24 to securely mate with the support member22. The depth of the bore 38 can also be over-extended so as to allow asignificant length of the mandrel 24 to penetrate or screw into the bore38. The bore 38 can also extend completely through the support member22. This would allow the length of the mandrel 24 to be adjusted toaccommodate stents of various sizes. The mandrel 24 also includes aplurality of ridges 25 that add rigidity and support to the stent 10during the coating process. The ridges 25 have a diameter of slightlyless than the inner diameter of stent 10. While three ridges 25 areshown, it will be appreciated by one of ordinary skill in the art thatadditional or fewer ridges may be present and they may be evenly orunevenly spaced.

The lock member 26 includes a coning end portion 42 tapering inwardly. Asecond end of the mandrel 24 can be permanently affixed to the lockmember 26 if the first end is disengagable from the support member 22.Alternatively, in accordance with another embodiment, the mandrel 24 canhave a threaded second end for screwing into a bore 46 of the lockmember 26. The bore 46 can be of any suitable depth that would allow thelock member 26 to be incrementally moved closer to the support member22. The bore 46 can also extend completely through the lock member 26.Accordingly, the stents 10 of any length can be securely pinched betweenthe support and the lock members 22 and 26. In accordance with yetanother embodiment, a non-threaded second end and the bore 46combination is employed such that the second end can be press-fitted orfriction-fitted within the bore 46 to prevent movement of the stent 10on the stent mandrel fixture 20.

Positioned a distance from the stent 10 (e.g., above the stent 10) is areservoir 210 holding a coating substance to be applied to the stent 10.The reservoir 210 is in fluid communication with an ejector 220 havingan aperture 230. The ejector 220 is also positioned a distance from thestent 10 (e.g., above, below and/or at an angle to the stent 10).Disposed within the ejector 220 is a transducer 410 (FIG. 4) thatconverts electrical energy into vibrational energy in the form of soundor ultrasound. The sound or ultrasound (collectively referred to asacoustic energy herein) ejects (or dispenses) drops of the coatingsubstance from the aperture 230 onto the stent 10. In an embodiment ofthe invention, each acoustic pulse from the transducer 410 dispenses asingle drop from the aperture 230.

The reservoir 210 dispenses the coating substance to the ejector 220,which ejects it through the aperture 230, which will be discussed infurther detail in conjunction with FIG. 4 below. The reservoir 210 candispense the coating substance using gravity and/or forced pressure(e.g., a pump) to the ejector 220. The aperture 230 has a small openingof 50 μm to 250 μm and therefore the coating substance will not exit theaperture 230 due to surface tension and/or gravity unless the transducer410 is activated. In an embodiment of the invention, if the ejector 220is positioned underneath the stent 10 with the aperture 230 pointingupwards, the ejector 220 can still be in the orientation shown in FIG. 4and gravity can be used to form a negative or positive meniscus byplacing the reservoir at a height above, even, or below the exitaperture 230. Further, a low surface energy coating, such as TEFLON, cancoat the aperture 230 to eliminate coating exiting the aperture exceptwhen desired. Accordingly, by using the transducer 410 during theapplication of the coating substance, the rate of coating dispensed canbe adjusted so that certain sections of the stent 10 receive morecoating than others. If the coating material is applied in anintermittent fashion, coating adjustments can be made during thestoppage of coating application. Further, the coating can be stoppedwhile the ejector 220 is being repositioned relative to the stent 10.

The ejector 220 is aligned with a stent strut 12 and coats eachindividual stent strut 12. As will be discussed further below, coatingflows into the ejector 220 and is ejected from the aperture 230 by thetransducer 410 onto the stent strut 12, thereby limiting the coating tojust the outer surface stent strut 12 and not other surfaces (e.g., theluminal surface) as in spaying and immersion techniques. In oneembodiment, the sidewalls of the stent struts 12 between the outer andinner surfaces can be partially coated. Partial coating of sidewalls canbe incidental, such that some coating can flow from the outer surfaceonto the sidewalls, or intentional.

Coupled to the ejector 220 can be a first imaging device 250 that imagesthe stent 10 before and/or after the coating substance has been appliedto a portion of the stent 10. The first imaging device 250, along with asecond imaging device 260 located a distance from the stent 10, are bothcommunicatively coupled to an optical feedback system 270 via wired orwireless techniques. The reservoir 210 may also be communicativelycoupled to the optical feedback system 270 via wired or wirelesstechniques. Based on the imagery provided by the imaging devices 250 and260, the optical feedback system 270 controls movement of stent 10 viathe motors 30A and 30B to keep the aperture 230 aligned with the stentstruts 12 and recoat the stent struts 12 if improperly (or inadequately)coated.

In an embodiment of the invention, the optical feedback system 270includes a network of components, at least one of which performsmovement while at least one other component determines the movement tobe made. In an embodiment of the invention, the optical feedback system270 can use other techniques besides optics to image a stent, such asradar or electron scanning

During operation of the stent coating apparatus 200, the opticalfeedback system 270 causes the imaging device 260 to image the fullsurface of the stent 10 as the feedback system 270 causes the motor 30Ato rotate the stent 10. After the initial imaging, the optical feedbacksystem 270, using the imaging device 260, aligns the aperture 230 with astent strut 12 by causing the motors 30A and 30B to rotate and translatethe stent 10 until alignment is achieved. The optical feedback system270 then causes the transducer 410 (FIG. 4) to dispense the coatingsubstance through the aperture 230 by emitting acoustic energy towardscoating substance located in the aperture 230. As the coating substanceis dispensed, the optical feedback system 270 causes the motors 30A and30B to rotate and translate the stent 10 in relation to the aperture 230so as to position uncoated sections of the stent strut 12 along theaperture 230, thereby causing the entire abluminal surface of the strut12 to be coated.

After a portion of the stent strut 12 has been coated, the opticalfeedback system 270 causes the transducer 410 to cease dispensing thecoating substance and causes the imaging device 250 to image the stentstrut 12 to determine if the strut 12 has been adequately coated. Thisdetermination can be made by measuring the difference in color and/orreflectivity of the stent strut 12 before and after the coating process.If the strut 12 has been adequately coated, then the optical feedbacksystem 270 causes the motors 30A and 30B to rotate and translate thestent 10 so that the aperture 230 is aligned with an uncoated stent 10section and the above process is then repeated. If the stent strut 12 isnot coated adequately, then the optical feedback system 270 causes themotors 30A and 30B to rotate and translate the stent 10 and thetransducer 410 to dispense the coating substance to recoat the stentstrut 12. In another embodiment of the invention, the optical feedbacksystem 270 can cause checking and recoating of the stent 10 after theentire stent 10 goes through a first coating pass.

In an embodiment of the invention, the imaging devices 250 and 260include charge coupled devices (CCDs) or complementary metal oxidesemiconductor (CMOS) devices. In an embodiment of the invention, theimaging devices 250 and 260 are combined into a single imaging device.Further, it will be appreciated by one of ordinary skill in the art thatplacement of the imaging devices 250 and 260 can vary as long as theyhave an acceptable view of the stent 10. In addition, one of ordinaryskill in the art will realize that the stent mandrel fixture 20 can takeany form or shape as long as it is capable of securely holding the stent10 in place.

Accordingly, embodiments of the invention enable the fine coating ofspecific surfaces of the stent 10, thereby avoiding coating defects thatcan occur with spray coating and immersion coating methods and limitingthe coating to only the abluminal surface and/or sidewalls of the stent10. In another embodiment, the coating can be limited to depots orpatterns as described in U.S. Pat. No. 6,395,326, which is incorporatedherein by reference. Application of the coating in the gaps 16 betweenthe stent struts 12 can be partially, or preferable completely, avoided.

After the brush coating of the stent 10 abluminal surface, the stent 10can then have the inner surface coated via electrospraying or spraycoating. Without masking the outer surface of the stent 10, bothelectrospraying and spray coating may yield some composition onto theouter surface and sidewalls of the stent 10. However, the inner surfacewould be substantially solely coated with a single composition differentfrom the composition used to coat the outer surface of the stent 10.Accordingly, it will be appreciated by one of ordinary skill in the artthat this embodiment enables the coating of the inner surface and theouter surface of the stent 10 with different compositions. For example,the inner surface could be coated with a composition having abio-beneficial therapeutic substance for delivery downstream of thestent 10 (e.g., an anticoagulant, such as heparin, to reduce plateletaggregation, clotting and thrombus formation) while the outer surface ofthe stent 10 could be coating with a composition having a therapeuticsubstance for local delivery to a blood vessel wall (e.g., ananti-inflammatory drug to treat vessel wall inflammation or a drug forthe treatment of restenosis).

The components of the coating substance or composition can include asolvent or a solvent system comprising multiple solvents, a polymer or acombination of polymers, a therapeutic substance or a drug or acombination of drugs. In some embodiments, the coating substance can beexclusively a polymer or a combination of polymers (e.g., forapplication of a primer layer or topcoat layer). In some embodiments,the coating substance can be a drug that is polymer free. Polymers canbe biostable, bioabsorbable, biodegradable, or bioerodable. Biostablerefers to polymers that are not biodegradable. The terms biodegradable,bioabsorbable, and bioerodable are used interchangeably and refer topolymers that are capable of being completely degraded and/or erodedwhen exposed to bodily fluids such as blood and can be graduallyresorbed, absorbed, and/or eliminated by the body. The processes ofbreaking down and eventual absorption and elimination of the polymer canbe caused by, for example, hydrolysis, metabolic processes, bulk orsurface erosion, and the like.

Representative examples of polymers that may be used include, but arenot limited to, poly(N-acetylglucosamine) (Chitin), Chitoson,poly(hydroxyvalerate), poly(lactide-co-glycolide),poly(hydroxybutyrate), poly(hydroxybutyrate-co-valerate),polyorthoester, polyanhydride, poly(glycolic acid), poly(glycolide),poly(L-lactic acid), poly(L-lactide), poly(D,L-lactic acid),poly(D,L-lactide), poly(D-lactic acid), poly(D-lactide),poly(caprolactone), poly(trimethylene carbonate), polyester amide,poly(glycolic acid-co-trimethylene carbonate), co-poly(ether-esters)(e.g. PEO/PLA), polyphosphazenes, biomolecules (such as fibrin,fibrinogen, cellulose, starch, collagen and hyaluronic acid),polyurethanes, silicones, polyesters, polyolefins, polyisobutylene andethylene-alphaolefin copolymers, acrylic polymers and copolymers otherthan polyacrylates, vinyl halide polymers and copolymers (such aspolyvinyl chloride), polyvinyl ethers (such as polyvinyl methyl ether),polyvinylidene halides (such as polyvinylidene chloride),polyacrylonitrile, polyvinyl ketones, polyvinyl aromatics (such aspolystyrene), polyvinyl esters (such as polyvinyl acetate),acrylonitrile-styrene copolymers, ABS resins, polyamides (such as Nylon66 and polycaprolactam), polycarbonates, polyoxymethylenes, polyimides,polyethers, polyurethanes, rayon, rayon-triacetate, cellulose, celluloseacetate, cellulose butyrate, cellulose acetate butyrate, cellophane,cellulose nitrate, cellulose propionate, cellulose ethers, andcarboxymethyl cellulose. Representative examples of polymers that may beespecially well suited for use include ethylene vinyl alcohol copolymer(commonly known by the generic name EVOH or by the trade name EVAL),poly(butyl methacrylate), poly(vinylidenefluoride-co-hexafluororpropene) (e.g., SOLEF 21508, available fromSolvay Solexis PVDF, Thorofare, N.J.), polyvinylidene fluoride(otherwise known as KYNAR, available from ATOFINA Chemicals,Philadelphia, Pa.), ethylene-vinyl acetate copolymers, and polyethyleneglycol.

“Solvent” is defined as a liquid substance or composition that iscompatible with the polymer and/or drug and is capable of dissolving thepolymer and/or drug at the concentration desired in the composition.Examples of solvents include, but are not limited to, dimethylsulfoxide,chloroform, acetone, water (buffered saline), xylene, methanol, ethanol,1-propanol, tetrahydrofuran, 1-butanone, dimethylformamide,dimethylacetamide, cyclohexanone, ethyl acetate, methylethylketone,propylene glycol monomethylether, isopropanol, isopropanol admixed withwater, N-methyl pyrrolidinone, toluene, and mixtures and combinationsthereof.

The therapeutic substance or drug can include any substance capable ofexerting a therapeutic or prophylactic effect. Examples of active agentsinclude antiproliferative substances such as actinomycin D, orderivatives and analogs thereof (manufactured by Sigma-Aldrich 1001 WestSaint Paul Avenue, Milwaukee, Wis. 53233; or COSMEGEN available fromMerck). Synonyms of actinomycin D include dactinomycin, actinomycin IV,actinomycin I₁, actinomycin X₁, and actinomycin C₁. The bioactive agentcan also fall under the genus of antineoplastic, anti-inflammatory,antiplatelet, anticoagulant, antifibrin, antithrombin, antimitotic,antibiotic, antiallergic and antioxidant substances. Examples of suchantineoplastics and/or antimitotics include paclitaxel, (e.g., TAXOL® byBristol-Myers Squibb Co., Stamford, Conn.), docetaxel (e.g., Taxotere®,from Aventis S.A., Frankfurt, Germany), methotrexate, azathioprine,vincristine, vinblastine, fluorouracil, doxorubicin hydrochloride (e.g.,Adriamycin® from Pharmacia & Upjohn, Peapack N.J.), and mitomycin (e.g.,Mutamycin® from Bristol-Myers Squibb Co., Stamford, Conn.). Examples ofsuch antiplatelets, anticoagulants, antifibrin, and antithrombinsinclude aspirin, sodium heparin, low molecular weight heparins,heparinoids, hirudin, argatroban, forskolin, vapiprost, prostacyclin andprostacyclin analogues, dextran, D-phe-pro-arg-chloromethylketone(synthetic antithrombin), dipyridamole, glycoprotein IIb/IIIa plateletmembrane receptor antagonist antibody, recombinant hirudin, and thrombininhibitors such as Angiomax ä (Biogen, Inc., Cambridge, Mass.). Examplesof such cytostatic or antiproliferative agents include angiopeptin,angiotensin converting enzyme inhibitors such as captopril (e.g.,Capoten® and Capozide® from Bristol-Myers Squibb Co., Stamford, Conn.),cilazapril or lisinopril (e.g., Prinivil® and Prinzide® from Merck &Co., Inc., Whitehouse Station, N.J.), calcium channel blockers (such asnifedipine), colchicine, proteins, peptides, fibroblast growth factor(FGF) antagonists, fish oil (omega 3-fatty acid), histamine antagonists,lovastatin (an inhibitor of HMG-CoA reductase, a cholesterol loweringdrug, brand name Mevacor® from Merck & Co., Inc., Whitehouse Station,N.J.), monoclonal antibodies (such as those specific forPlatelet-Derived Growth Factor (PDGF) receptors), nitroprusside,phosphodiesterase inhibitors, prostaglandin inhibitors, suramin,serotonin blockers, steroids, thioprotease inhibitors,triazolopyrimidine (a PDGF antagonist), and nitric oxide. An example ofan antiallergic agent is permirolast potassium. Other therapeuticsubstances or agents which may be appropriate agents include cisplatin,insulin sensitizers, receptor tyrosine kinase inhibitors, carboplatin,alpha-interferon, genetically engineered epithelial cells, steroidalanti-inflammatory agents, non-steroidal anti-inflammatory agents,antivirals, anticancer drugs, anticoagulant agents, free radicalscavengers, estradiol, antibiotics, nitric oxide donors, super oxidedismutases, super oxide dismutases mimics,4-amino-2,2,6,6-tetramethylpiperidine-1-oxyl (4-amino-TEMPO),tacrolimus, dexamethasone, ABT-578, clobetasol, cytostatic agents,prodrugs thereof, co-drugs thereof, and a combination thereof. Othertherapeutic substances or agents may include rapamycin and structuralderivatives or functional analogs thereof, such as 40-O-(2-hydroxy)ethyl-rapamycin (everolimus), 40-O-(3-hydroxy)propyl-rapamycin,40-O-[2-(2-hydroxy)ethoxy]ethyl-rapamycin, and 40-O-tetrazole-rapamycin.

FIG. 3 is a block diagram illustrating a stent coating apparatus 300according to another embodiment of the invention. The stent coatingapparatus 300 is similar to the stent coating apparatus 200. However,the ejector 220 is capable of translational movement along a guide rail310. Accordingly, the alignment of the aperture 230 with a stent strut12 is accomplished by the optical feedback system 270 causing the engine30A to rotate the stent 10 in combination with causing the brushassembly 230 to move along the guard rail 310. The guard rail 310 shouldbe at least about as long as the stent 10 to enable the ejector 220 fullmobility over the length of the stent 10. In some embodiments, theejector 220 is capable of translational movement along the guide rail310 in combination contemporaneously or in turn with rotation andtranslation of the stent 10.

In another embodiment of the invention, the ejector 220 is coupled to apainting robot, such as one have six axes (three for the base motionsand three for applicator orientation) that incorporates machine visionand is electrically driven. Accordingly, the ejector 220 can fullyrotate around and translate along a stent 10 in a stationary position.Alternatively, both the ejector 220 and the stent 10 can rotate and/ortranslate contemporaneously or in turn. For example, the ejector 220 canmove for alignment with a strut of the stent 10 while the stent 10 canmove during coating after alignment, vice versa, or a combination ofboth.

In any of the above-mentioned embodiments, the coating process can becontinuous, i.e., the ejector 220 can move along and coat the entirestent 10 without stopping, or move intermittently, i.e., coating a firstsection of the stent 10, stopping, and then aligning with a secondsection of the stent 10, and coating that second section. The secondsection may be adjacent to the first section or located a distance fromthe first section.

FIG. 4A is a diagram illustrating cross section of the ejector 220having the aperture 230 and the transducer 410 according to anembodiment of the invention. The ejector 220 includes a transducersystem 400 including the transducer 410, which can be piezoelectric, acavity 420, and an acoustic lens 430. The transducer 410 is positioned adistance from the aperture 230. The transducer 410 converts electricalenergy into unidirectional acoustic energy, which travels through thecavity 420 and is focused on the aperture 230 where the fluid meniscusis located by the acoustic lens 430. The acoustic lens 430 can beconcave in shape. The focused energy causes an increase in pressure tocause droplets to drop off. The transducer 410 can include (or becoupled to) drive electronics, such as power supplies, RF amplifier, RFswitches, and pulsers; an acoustic lens assembly; a fluid reservoir andlevel control hardware; and/or an imaging system for online monitoringfor drop size and velocity. As the reservoir constantly feeds thecoating substance to the ejector 220 during coating applications, themeniscus stays level, thereby preventing the need for the transducer 410to be refocused. While the ejector 220 is shown with the aperture 230facing downwards, it will be appreciated by one of ordinary skill in theart that the ejector 220 can employed with the aperture 230 facingupwards or otherwise positioned with respect to the stent 10.

The acoustic energy causes the ejection of drops of the coatingsubstance due to an acoustic pressure transient at the meniscus andprevents clogging of the aperture 230 since the ejected drops do notcome in contact with the aperture 230 during ejection. The acousticenergy can have a frequency of about 500 Hz to about 5000 Hz. The firingrate can range from about 1 to 3000 Hz. In an embodiment of theinvention, the aperture 230 has a diameter of less than about 20microns, leading to drops with a maximum diameter about 20 microns. Inanother embodiment of the invention, the aperture 230 has a diameter ofabout 10 microns to about 50 microns, yielding similar-sized drops. Dropvolume can range from about 5 picoliters to about 30 picoliters. Dropdiameter decreases exponentially as frequency increases. Pulse widthscan vary from about 10 μsec to about 60 μsec.

FIG. 4B is a diagram illustrating another embodiment of the transducersystem 400. The transducer system 400 transmits acoustic energy to themeniscus of a coating substance (shown in black) at an aperture 450 of aplate 440.

FIG. 5 is a block diagram illustrating a stent coating apparatus 500according to another embodiment of the invention. The stent coatingapparatus 500 is similar to the stent coating apparatus 200. However, inplace of the reservoir 210 is a reservoir housing 510 having a pluralityof reservoirs 605 (FIG. 6) (e.g., wells) located beneath the stent 10.The reservoirs 605 each hold a coating substance. A transducer 520 islocated beneath the reservoir housing 510 and is not in contact with thecoating substance. The transducer 520 is substantially similar to thetransducer 410 and transmits acoustic energy at one of the plurality ofreservoirs 605 focused on the surface of the coating substance, as willbe discussed in further detail below.

FIG. 6 is a diagram illustrating a cross section an ejector comprisingthe reservoir housing 510 and the transducer 520. The transducer 520outputs acoustic energy at a reservoir 605 focused at the surface of thecoating substance 600 therein. Each pulse ejects a known amount of thesubstance 600 in a droplet 620 from the reservoir onto the stent 10,thereby decreasing the substance 600 level in the reservoir 605.Accordingly, after each pulse of acoustic energy, the transducer 520 canbe refocused to the new level in the reservoir 605. In an alternativeembodiment, the reservoirs can be constantly refilled, thereby keepingthe substance 600 level the same throughout the stent 10 coatingprocess. In an embodiment of the invention, the reservoirs 605 can eachhold different coating substances, e.g., a first reservoir can holdsubstance 600 while a second reservoir can hold substance 610. Thetransducer 520 can then cause the ejection of different coatingsubstances onto the stent 10 during a single application process.Further, as there is no contact between the transducer 520 andreservoirs 605, there is no chance of cross contamination betweenreservoirs 605 or clogging of any ejectors.

In an embodiment of the invention, the apparatus 500 further includes athird imaging device 630 positioned to image the fluid meniscus in thereservoirs 605. The imaging device 630 is communicatively coupled to theoptical feedback system 270, which is further capable of determining theheight of the fluid meniscus in the reservoirs 605 and adjusting thetransducer 520 accordingly (e.g., moving the transducer 520 vertically)to maintain focus on the fluid meniscus as the fluid meniscus moves toensure optimal drop size and velocity.

In the embodiment shown in FIG. 7, one or more of the reservoirs 605 maycontain two different coating substances, e.g., the coating substance610 and a coating substance 710. The transducer 520 ejects a combineddrop 720 from the reservoir by focusing a pulse of acoustic energy atthe interface between the two substances. Accordingly, the stent 10 canbe coated simultaneously with two different coating substances.

FIG. 8 is a flowchart illustrating a method 800 of coating an abluminalstent surface. In an embodiment of the invention, the system 200, 300 or500 can implement the method 800. First, an image of the stent 10 iscaptured (810) as the stent 10 is rotated. Based on the captured image,an ejector is aligned (820) with a stent strut 12 of the stent 10 viarotation and/or translation of the stent 10 and/or translation/rotationof the transducer. A coating is then dispensed (830) onto the stent viaacoustic ejection of a coating substance. As the coating is beingdispensed (830), the ejector and/or stent are moved (840) relative toeach other so as to coat at least a portion of the stent strut 12. Thecoating process could involve vision guided motion such that the stentis coated as the vision system guides the stent under the nozzle or thenozzle over the stent. Alternatively, the vision system could image theentire stent first then cause the stent to move under the nozzle or thenozzle over the stent for the duration of the coating process.

The dispensing is then stopped (845), and an image of at least a portionof the stent that was just coated in captured (850). Using the capturedimage, the coating is verified (860) based on color change, reflectivitychange, and/or other parameters. If (870) the coating is not verified(e.g., the stent strut 12 was not fully coated), then the strut 12 isrecoated (890) by realigning the transducer with the strut 12,dispensing the coating, and moving the ejector relative to the strut.Capturing (850) an image and verifying (860) are then repeated.

If (870) the coating is verified and if (880) the stent has beencompletely coated, then the method 800 ends. Otherwise, the method 800is repeated with a different stent strut starting with the aligned(820).

In an embodiment of the invention, the luminal surface of the stent 10can then be coated with a different coating using electroplating orother technique. Accordingly, the abluminal surface and the luminalsurface can be coated with different coatings. Further, the entire stent10 can be coated (830) before verification (860) of the entire stent 10or portions thereof.

While particular embodiments of the present invention have been shownand described, it will be obvious to those skilled in the art thatchanges and modifications can be made without departing from thisinvention in its broader aspects. For example, multiple reservoirs andtransducers can be used simultaneously to speed up the coating of astent. Further, the multiple reservoirs can contain different coatingsubstances such that different coating substances can be applied todifferent regions of a stent substantially simultaneously. Therefore,the appended claims are to encompass within their scope all such changesand modifications as fall within the true spirit and scope of thisinvention.

1. A stent coating apparatus, comprising: a transducer capable ofejecting droplets of a coating substance from a reservoir; and anoptical feedback system that aligns the transducer with a stent strutsuch that the coating substance is delivered to a stent strut.
 2. Theapparatus of claim 1, wherein the optical feedback system causes themovement of the transducer relative to the stent strut while the coatingis being delivered.
 3. The apparatus of claim 1, wherein the opticalfeedback system aligns the transducer with the stent strut via rotationand translation of the stent.
 4. The apparatus of claim 1, wherein theoptical feedback system aligns the transducer with the stent strut viarotation of the stent and translation of the transducer.
 5. Theapparatus of claim 1, wherein the optical feedback system verifies thecoating on the stent strut and causes recoating of the stent strut ifthe coating is determined to be inadequate.
 6. The apparatus of claim 1,wherein energy from the transducer is focused on a fluid meniscus of thecoating substance.
 7. The apparatus of claim 6, wherein the opticalfeedback system is positioned to view the fluid meniscus and furthercapable of moving the transducer relative to the fluid meniscus tomaintain focus on the fluid meniscus.
 8. The apparatus of claim 1,wherein energy from the transducer is focused at the interface of thecoating substance and a second coating substance in the reservoir. 9.The apparatus of claim 1, wherein the transducer is located within anejector holding the coating substance.
 10. The apparatus of claim 1,wherein the transducer is external to a reservoir housing holding thereservoir.
 11. The apparatus of claim 1, wherein the transducer isexternal to a reservoir housing holding a plurality of coatingsubstances in individual reservoir compartments.